1. Field of the Invention
The present invention relates to an ink jet printing method and an ink jet printing apparatus and, more particularly, to an ink jet printing method and an ink jet printing apparatus for performing so-called preliminary ejection, in which ink is ejected from a printing head unrelated to printing, while printing an image.
Also, the present invention can be applied to apparatuses such as a printer, a copying machine, a facsimile machine having a communication system, a word processor having a printer section and so on for printing on a medium to be printed such as paper, yarn, fiber, fabric, metal, plastic, rubber, glass, wood, ceramics and so on and, moreover, industrial printing apparatuses combined complexly with various processing units.
It should be appreciated that “printing” in the present specification means not only to afford images having a meaning such as characters and graphics to the medium to be printed, but also to afford images having no meaning such as patterns.
2. Detailed Description of the Related Art
The preliminary ejection is performed to discharge highly viscous ink and dust in an ink ejection orifice of a printing head through ink ejection thereof so as to keep the ejection performance of a printing head satisfactory. It is also executed for avoiding density unevenness on a printed image by ejecting ink whose concentration of color material such as dye and pigment has increased. A usual manner of such preliminary ejection is that, in the case of serial method of printing by causing the printing head to scan, the ink ejection is performed, for the preliminary ejection, to an ink receptacle disposed at one end of the scanning area. Further, in the case of full line method for printing by moving a printing medium with respect to a printing head whose ink ejection orifices are arranged in correspondence to the width of the printing medium, the ink receptacle is moved relatvely to the printing head to oppose thereto and ink is ejected to the same.
On the other hand, those of which ink is ejected for the preliminary ejection while an image is printed on the printing medium are also known. For instance, it is described to perform the preliminary ejection at a constant frequency for the Ink ejection for printing, in Japanese Patent Application Laid-Open No. 1980-139269. According to such preliminary ejection, it is not necessary for the printing head to move for preliminary ejection as in the case of performing the preliminary ejection to a predetermined ink receptacle disposed in the printer. Therefore, it becomes possible to prevent the throughput of printing from lowering as much. Even when the ejection is not performed for certain ejection orifices during the printing in relation with the printing data, the preliminary ejection can be performed for these ejection orifices, because this method for performing the preliminary ejection to the printing medium (also referred as “paper preliminary ejection” in the present specification) is performed, basically, with accompanying the ink ejection for printing an image. More specifically, during the printing, the printing is performed in a state where the printing head is not covered with a cap or the like and the ejection orifice part is exposed, and in this case, even when the ejection is not performed for certain ejection orifices according to the printing data, the ink ejection through preliminary ejection can be performed for these ejection orifices, allowing to effectively prevent ejection failure due to the exposed state.
Particularly, the paper preliminary ejection is effective in the case of printing on a relatively large sized printing medium. More specifically, in the case of printing on a large sized printing medium, the throughput tends to lower because as much time is necessary for the printing head to scan. However, the paper preliminary ejection can partly replace normal preliminary ejection, which is performed at a predetermined position in a printing apparatus, or can be performed in place of the normal preliminary ejection. Thereby, time period for the normal preliminary ejection can be decreased as much and thus lowering of the throughput can be prevented. In addition, on focusing attention on an ejection orifice in the printing head, a non-ejection state of the ejection orifice, for which print data represents “non-ejection”, may continue, and then ink ejection from the ejection orifice may be executed by that the print data represents “ejection” during scanning of the printing head in the non-ejection state. In such case, when printing on a large sized printing medium, the ejection orifice in the printing head remains exposed for a long period of time. For this condition, the paper preliminary ejection is performed and then first ejection for printing after the exposed state can be well executed.
However, when the paper preliminary ejection is performed for different colors of inks without variation, unnecessary preliminary ejection may be performed and ink may be used wastefully. More specifically, a property of ink affecting ink ejection by the printing head, such as a degree of viscosity increasing of ink, generally depends on colors of ink. In such case, when the paper preliminary ejection of a constant period is performed for a plurality of colors of inks without variations, the paper preliminary ejection for the ink which does not increase viscosity during such constant period is also performed, and then the ink as much is used wastefully.
Particularly in the case of using both the normal preliminary ejection which is performed at a predetermined location in a printing apparatus and the paper preliminary ejection, there may be a case that depending on a color of ink, an ejection performance of a printing head for ejecting the color of ink can be maintained well only by the normal preliminary ejection. In this case, it is desirable that the paper preliminary ejection for the color of ink is not performed in terms of decreasing ink use for the preliminary ejection. A reason that properties of inks, such as viscosity increasing, affecting ink ejection by the printing head differ depending on colors of ink is that the properties differ depending on color materials in ink such as dye and pigment, and contents of the color materials of the same color inks, and further differ depending on other solvent in ink.
Further, the above discussion is the case with ejection amounts different for each printing head. Generally, the greater an amount (a volume of an ink droplet) of one time ejection is, the longer the time period during which a factor causing a ejection failure, such as increasing of ink viscosity, does not occur. Therefore, when the paper preliminary ejection of the constant period is performed for the plurality of colors of ink without variations, ink may be used wastefully for the printing head ejecting such greater amount of ink.